Joint signal-idler photoelectron distributions of twin beams have been measured recently in two distinct regimes:
either the mean number of photon pairs per one pump pulse is lower that the number of independent modes or
vice versa. Exploiting a microscopic quantum theory for joint quasi-distributions in parametric down-conversion
based on the model of superposition of signal and noise we characterize properties of twin beams in terms of quasidistributions
using experimental data. In parallel to the microscopic model, joint signal-idler photon-number
distribution is reconstructed using the method of maximum likelihood. Negative values as well as oscillating
behavior in quantum region are characteristic for the joint signal-idler quasi-distributions of integrated intensities.
The larger the mean number of photon pairs per mode the weaker the quantum features are. However, they
survive even in the mesoscopic regime, i.e. when tens of photon pairs per mode are present on average. Also
the conditional and difference photon-number distributions are shown to be sub-Poissonian and sub-shot-noise,
respectively. Violation of classical inequalities for photon-number distributions is discussed.